This invention relates to a thermal protector device comprising a polymeric PTC element. More particularly, this invention relates to a thermal protector device comprising a polymeric PTC element wherein said element is protected from external forces, especially shear forces, that would otherwise significantly degrade electrical performance of the element.
Thermal protector devices comprising PTC elements are well known. These devices generally comprise a substantially planar polymeric PTC element provided on each broad surface with a conductive foil, and having an electrical terminal soldered to each conductive foil such that the terminals are in electrical contact with the PTC element through the conductive foil. It is further known that the PTC effect of such devices can be significantly degraded when the PTC elements thereof are subjected to mechanical forces applied through one or both of the electrical terminals, such as the shear forces that may occur when the devices are mechanically mounted into an electrical circuit. PTC elements comprising cross-linked polymer are particularly susceptible to such performance degradation.
One prior art solution to the problem, as disclosed in U.S. Pat. No. 4,698,614, issued to Welch et al. and assigned to the common assignee, involves thermal protector device configurations wherein the terminals on either side of the PTC element are mechanically clamped together in such a way that the PTC element is essentially protected against foreign external mechanical forces. In another solution, disclosed in pending U.S. patent application Ser. No. 109,105 filed Dec. 3, 1987 by Yagher, Jr., and also assigned to the common assignee, at least one of the terminals includes a self-supporting spring which provides play between the thermal protector device and the circuit element to which it is mounted. While each of the aforementioned solutions adequately protects the PTC element from deleterious mechanical forces such as shear forces, each also requires the use of specially designed terminals or terminal attachments.
It is thus one object of the invention to provide a PTC thermal protector device wherein the PTC element is protected from external mechanical forces that would otherwise significantly degrade electrical performance of the element, and which does not require the use of specially designed terminals or terminal attachments.
It is yet another object of the invention to provide a PTC thermal protector device wherein the PTC element is protected from external mechanical forces that would otherwise significantly degrade electrical performance of the element, yet which device is simple and easy to assemble on a mass-production basis.
Other objects, advantages, and novel features of the invention will be readily apparent to those skilled in the art in light of the following description and figures.